I have read almost every post since the beginning of this thread and have some comments.
I do not think that soldered joints are as bad as you stated if you follow certain rules. The marine type wires are tinned that makes them good candidate for such operation. The best electrical characteristic has solder with 100% tin. However, it has also weak mechanical properties and can crystallize over the years. To improve the solder characteristics copper and silver is added. You should use SnAgCu type of solder. Now to the flux. First of all - NO ACID OR CHLORIDE FLUX can be used on electrical type connections. If you would like to make good, durable connections you should use solder with ROSIN core as flux.
I know that to make a good solder connection is not easy. The solder melting temperature should be in the range of 270 - 320C. It can't be too low because the connection can fail just after. If the temperature is too high you will melt the wire insulation and causes wire oxidization. It means that a properly made joint requires some experience. Crimping process is faster and requires less experince (sorry dave.). As for the mechanical strength of, say, 14AWG wire connection - good, adhesive filled heatshrink tube will do just perfect to make such connection impenetrable to water. If you are still hesitant - use two tubes (the external one slightly longer). It works perfectly on cables 230,000V ( when submerged in 4ft of water) so .. I think it will work on 12V too. It will not only make the joint waterproof but also add mechanical strength to the exposed wires. Properly made soldered joint should survive many years.
This are my 2c.
PS - I wouldn't leave a crimmped connector without some sort of stiffening of the whole assembly.